Method of oxydehydrogenation of alkyl aromatic compounds

ABSTRACT

Magnesium nickel pyrophosphate is a superior catalyst for oxydehydrogenating alkyl aromatic compounds including nitrogen heterocyclics which have at least one C2-C6 alkyl side chain to form derivatives having side chain unsaturation. The alkyl aromatic compound can have one to two rings. The process is carried out at 450*-650*C. and a space velocity of 55-2500.

'United States Patent [191 Vrieland et al.

11] 3,917,732 Nov. 4, 1-975 METHOD OF OXYDEHYDROGENATION OF ALKYL AROMATIC COMPOUNDS [75] Inventors: G. Edwin Vrieland, Midland, Mich.; Hans R. Friedli, Lake Jackson, Tex.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: May 28, 1974 [21] Appl. No.: 474,124

[52] US. Cl. 260/669 R; 252/437 [51] Int. Cl. C07C 5/48 [58] Field of Search 252/437, 669 R, 683.3

[56] References Cited UNITED STATES PATENTS 2,945,900 7/1960 Alexander et al 260/669 R 3,308,193 3/1967 Bajars.....' 260/680 D 3,641,180 2/l972 Stowe et al. 3,793,225 2/1974 Bertus et al 252/437 Primary Examifief-Paul M. Coughlan, Jr. Attorney, Agent, or FirmStephen Hoynak [57] ABSTRACT 10 Claims, No Drawings METHOD OF oxvusuvosoosusrlouor ALKYL AROMATIC COMPOUNDS BACKGROUND OF THE INVENTION Certain alkaline earth-nickel phosphates, such as calcium-nickel phosphate or strontium-nickel phosphate are good dehydrogenation catalysts for converting n-. butenes to .butadiene'or for oxydehydrogenating. lower aliphatic alkanes and alkenes to dienes. Although they also dehydrogenate alkyl aromatic hydrocarbons to their alkene aromatic derivatives, these catalysts are not as active for this purpose, as are the well-known self-regenerativecatalysts containing iron, zinc or magnesium oxides and potassium oxide or a potassium compound convertible to the oxide.

One of the shortcomings of the self-regenerative dehydrogenation catalysts for converting ethylbenzene to styrene is that under acceptable commercially operating conditions the conversion of the ethylbenzene is in the 35-40% range. Selectivity, however, is in the 85-95% range. The self-regenerative catalysts are not sufficiently selective in oxydehydrogenation systems to be useful commercially for converting alkyl benze'nes to alkene derivatives in the presence of oxygen.

Therefore, an object of this invention is the provision of a superior catalyst for oxydehydrogenation of an alkyl aromatic compound. Another object is to provide a process for oxydehydrogenating alkyl aromatic compounds in which process superior conversions with high selectivities of the alkyl group to an alkene group are obtained.

SUMMARY OF THE INVENTION This invention concerns a novel catalyst and a method of oxydehydrogenating alkyl aromatic compounds having at least one C -C alkyl group, including nitrogen heterocyclics, and one to two rings in the aromatic moiety, to form derivatives having aliphatic unsaturation in the side chain. More particularly, the catalyst is magnesium-nickel pyrophosphate which has been impregnated with phosphate ions. The catalyst can also contain small amounts of chromium oxide. The method comprises passing a mixture of an oxygen containing gas, and vapors of the alkyl aromatic compounds, with or without an inert diluent vapor, over the catalyst at a temperature of from about 450C. to about 650C., at a space velocity of from about 55 to about 2500.

DETAILED DESCRIPTION OF THE INVENTION The novel magnesium-nickel pyrophosphate catalyst of this invention can contain from about 6 to about 9.5 atoms of Mg per atom of nickel.

The catalyst can be prepared by the general procedure described in US. Pat. No. 2,542,813 by commingling a mixture of Ni(NO Mg(NO and H PO with 1. 69.3 g .-Mg(NO3) .6H O and 8.72 g. Ni(NO .6- l-l O-was added; to 250 cc water and the pH was adjusted to 6.5 with Nl-hOl-l. 1

2. A solution of 44.6 g. (NHMHPO, in 250 cc water was neutralized to pH 7 with nitric acid.-

3. .Solution 1 was added to solution 2 with rapid stirring. Ammonium hydroxide was added slowly to maintain the pHat about6. M

The precipitate was filtered, dried and calcined at 550C. to form a magnesium-nickel pyrophosphate in which the Mg to nickel mol ratio was about 9 to 1.

The molar ratio of oxygen to alkyl aromatic compound can range from about 0.5 to about 4.0 moles of 0 per mol of alkyl aromatic compound, buta preferred range is from about 0.5 to about 1.5 and most preferred is a range of about 0.9 to about 1.1 mols 0 per mol of aromatic compound.

The oxygen can be pure oxygen air or air enriched with oxygen.

The space velocity (vol./vol./hr.) can range from about 55 to 2500, but a preferred range is from about 250 to about 1800. Most preferred is a range of from about 800 to about 1800.

Diluents when used can be the noble gases, nitrogen, carbon dioxide or steam. These can range from about 4-16 volumes per volume of alkyl aromatic compound, but preferably range from about 4 to about 1 1 volumes.

The pressure at which the reaction can be run ranges from 0.5 to about 5 atmospheres, but it is preferable to operate at autogenous pressure which is generally the range of about 1 to about 2 atmospheres.

The reaction can be effected in a temperature range of from about 450C. to about 650C., but a preferred range is from about 500C. to about 650C.

Care should be exercized to avoid explosive mixtures when feeding the alkyl aromatic compound and oxygen into the reactor.

The examples which follow are intended to illustrate, but not to limit the invention. All parts are by weight unless specifically indicated otherwise.

The reactor for this example was a high silica glass tube 16 mm ID. and 42 cm. long, with an inlet for the compound to be dehydrogenated and another for a premixed feed of oxygen and an inert diluent. After loading the reactor with catalyst, coarse, high silica chips were placed above the catalyst layer to serve as a mixing and preheating area. The reactor was heated by placing it in an electric resistance furnace.

The reactor was loaded with 20 ml. of the magnesium-nickel pyrophosphate catalyst, described above, and then high silica chips were loaded on top of the catalyst. The outlet from the reactor had a valved line connected to a vapor phase chromatograph, in which 0,, N CO, CO, and benzene, toluene, alkyl aromatic and alkegyl aromatic hydrocarbon in the effluent were analyze A mixture of cc helium, 15 cc O and 15 cc ethyl benzene (STP) per minute was fed to the reactor. The reaction temperature was 533C. The conversion of ethyl benzene was 70.2% and the selectivity to styrene was 90.2% after 2 /2 hours of operation.

The GSHV of this example was about 360 hr.

We claim:

1. A method of oxydehydrogenating ethyl benzene to form styrene comprising feeding a mixture of from about 0.5 to about 4.0 moles of oxygen per mole of ethyl benzene into contact with a catalyst consisting essentially of magnesium nickel pyrophosphate having 3 from about 6 to about 9.5 atoms of magnesium per atom of nickel at a reaction temperature of from about 450 to about 650C, and a space velocity of from about 55 to about 2500 and'recovering the styrene from the effluent.

2. The method of claim 1 in which the reaction temperature is from about 500C. to about 650C.

3. The method of claim 1 in which the molar ratio of oxygen is from about .5 to 1.5 mols per mol of ethyl benzene.

4. The method of claim 3 in which molar ratio of oxygen is from about 0.9 to about 1.1 per mole of ethyl benzene.

5. The method of claim 1 in which the catalyst is magnesium nickel pyrophosphate having a Mg to Ni mole ratio of 9 to 1, the feed contains 6.0 volumes of an inert diluent and 1.0 volume of oxygen per volume of vaporized ethyl benzene and the space velocity is about 55 to about 2500.

6. The method of claim 5 in which the inert diluent is helium.

7. The method of claim 5 in which the inert diluent is nitrogen.

8. The method of claim 5 in which the space velocity ranges from about 250 to about 1800.

9. The method of claim 5 in which the inert diluent is steam.

10. The method of claim 8 in which the space velocity ranges from about 800 to about 1800. 

1. A METHOD OF OXYDEHYDROGENATING ETHYL BENZENE TO FORM STYRENE COMPRISING FEEDING A MIXTURE OF FROM ABOUT 0.5 TO ABOUT 4.0 MOLES OF OXYGEN PER MOLE OF ETHYL BENZENE INTO CONTACT WITH A CATALYST CONSISTING ESSENTIALLY OF MAGNESIUM NICKEL PYROPHOSPHATE HAVING FROM ABOUT 6 TO ABOUT 9.5 ATOMS. OF MAGNESIUM PER ATOM OF NICKEL AT A REACTION TEMPERATURE OF FROM ABOUT 450* TO ABOUT 650*C., AND A SPACE VELOCITY OF FROM ABOUT 55 TO ABOUT ABOUT 2500 AND RECOVERING THE STYRENE FROM THE EFFLUENT.
 2. The method of claim 1 in which the reaction temperature is from about 500*C. to about 650*C.
 3. The method of claim 1 in which the molar ratio of oxygen is from about .5 to 1.5 mols per mol of ethyl benzene.
 4. The method of claim 3 in which molar ratio of oxygen is from about 0.9 to about 1.1 per mole of ethyl benzene.
 5. The method of claim 1 in which the catalyst is magnesium nickel pyrophosphate having a Mg to Ni mole ratio of 9 to 1, the feed contains 6.0 volumes of an inert diluent and 1.0 volume of oxygen per volume of vaporized ethyl benzene and the space velocity is about 55 to about
 2500. 6. The method of claim 5 in which the inert diluent is helium.
 7. The method of claim 5 in which the inert diluent is nitrogen.
 8. The method of claim 5 in which the space velocity ranges from about 250 to about
 1800. 9. The method of claim 5 in which the inert diluent is steam.
 10. The method of claim 8 in which the space velocity ranges from about 800 to about
 1800. 